This invention relates to a new pressure swing adsorption process for separating at least one component from a gas mixture. More particularly, it is concerned with an improvement in a separation process for a gas mixture, for example, in recovering or collecting nitrogen from air, which nitrogen is a selectively adsorbable component contained therein, by the use of an adsorbent such as zeolite.
As a separation process for a gas mixture there has heretofore been known the pressure swing adsorption process in which the following steps as fundamental steps are repeated successively in order, an adsorption step wherein a selectively adsorbable component contained in a gas mixture is selectively adsorbed on an adsorbent by an increase in pressure, a purge step wherein a purge gas enriched with the selectively adsorbable component is introduced onto the adsorbent to concentrate the selectively adsorbable component, and a desorption step wherein the gas enriched with the selectively adsorbable component is desorbed from the adsorbent with pressure reduction, (for example, see U.S. Pat. Nos. 3,797,201 and 4,070,164).
In such pressure swing adsorption process, in case a portion of the gas enriched with a selectively adsorbable component desorbed in the desorption step is recovered and the remaining portion is used as a purge gas in the purge step, it is necessary that the desorbed gas to be used as the purge gas should be increased in pressure at least up to the purge step pressure And once the said purge gas is introduced into an adsorption column for carrying out the purge step, a less selectively adsorbable component in the column is expelled and a gas enriched with the less selectively adsorbable component is discharged from the adsorption column. Although this effluent gas has substantially the same pressure as the purge gas, such pressure is not utilized at all, and this is the actual situation.
It is an object of this invention to provide an improved pressure swing adsorption process for separating a gas enriched with at least one selectively adsorbable gaseous component from a gas mixture.
It is another object of this invention to provide a more efficient separation process for a gas mixture by utilization of the pressure of an effluent gas.
Other objects and advantages of this invention will become apparent from the following description.